Pesticides applied to millions of acres of corn and soybeans are seeping into drinking water supplies across the Midwest, posing serious health risks including birth defects and cancer. A new scientific review from the Rodale Institute reveals that conventional farming practices, particularly the widespread use of seed-coating insecticides and herbicides, are driving contamination that existing water treatment systems cannot fully remove. The problem is so severe that in 2025, Iowa's largest city, Des Moines, had to impose lawn watering bans when its freshwater sources contained nearly twice the EPA's safe nitrate limit.

What Pesticides Are Contaminating Midwest Drinking Water?

Two pesticides dominate the contamination picture. Neonicotinoids, a class of insecticides used as seed coatings on the majority of corn and soybeans planted in the Midwest, are highly water-soluble and leach into surface water and groundwater. Research shows that neonicotinoids in drinking water sources increase the risk of birth defects in humans. The herbicide atrazine, linked to early-onset lung and prostate cancer as well as fertility problems and birth defects, is the most commonly detected pesticide in drinking water. Every year, 40 million Americans drink water containing measurable levels of atrazine, even though it is banned in most other developed countries.

Glyphosate, the most common herbicide used in the United States, presents another widespread concern. Its use has risen 15-fold since genetically modified herbicide-tolerant crops were introduced, and it now appears in over 70 percent of all water samples collected across the United States, including rain. Glyphosate is found in over 80 percent of all Americans surveyed. Recent research has associated glyphosate and other pesticides with increased cancer rates in major agricultural regions that are on par with the risk of smoking.

How Do Farm Chemicals End Up in Drinking Water?

The pathway from field to tap is straightforward but difficult to stop. In conventional no-till farming systems that rely on intensive herbicide applications, higher concentrations of atrazine are found throughout the soil profile. Between 3 and 9 percent of the applied herbicide amount is transported through the soil, eventually contaminating drinking water supplies. In the Midwest's rainy, tile-drained landscapes, nitrates and pesticides leach through the soil profile and are exported via tile drains and groundwater outlets rather than remaining on the surface.

A recent scientific review from Polk County, Iowa, attributed 80 percent of nitrate contamination in Des Moines' freshwater sources to upstream agricultural sources such as nitrogen fertilizer and manure. The problem has worsened with climate variability. Heavy rain events following drought years now routinely flush accumulated nitrate into rivers and aquifers, pushing many private wells and municipal systems across the region above EPA limits. In 2026, unusually high levels of nitrate in freshwater sources during winter caused nitrate removal to begin in January for the first time since 2015, and by the end of April, data from the Iowa Water Quality Information System estimated that over 100 million pounds of nitrogen would have entered freshwater sources in Iowa alone.

What Are the Health Risks?

The health consequences are significant and well-documented. Pesticides that are endocrine disruptors, meaning they interfere with hormone systems, or known or suspected carcinogens are commonly found in surface water and drinking water sources. Neonicotinoids disrupt soil food webs and harm aquatic ecosystems when they leach into surface water. Beyond pesticides, nitrate pollution in drinking water causes serious harm. Every year, over 12,000 new cancer cases can be attributed to nitrate pollution in water, with agricultural runoff being the primary source. In Iowa, pesticides and nitrates are two of the primary risk factors contributing to the state's cancer rate, which is increasing and is the second-highest in the country.

Rural communities are most vulnerable. Smaller rural communities lack the resources needed to treat water when faced with chronic contamination, forcing residents to rely on bottled water or unsafe taps for extended periods. Even sophisticated treatment systems struggle. Despite having one of the most advanced nitrate removal systems in the world, Des Moines Water Works could not provide enough clean water when its freshwater sources contained almost twice the regulated limit of nitrate.

Why Current Solutions Are Failing

The scientific consensus is clear: edge-of-field mitigation strategies, such as constructed wetlands or buffer strips placed at the edge of agricultural land, have failed to achieve meaningful improvements at scale. These approaches treat the symptom, not the cause. The real solution requires transforming how farms operate from the ground up, shifting from intensive chemical-dependent systems to practices that protect water at the source.

How to Reduce Pesticide and Nitrate Contamination in Drinking Water

• In-Field Crop Diversification: Transitioning from monoculture corn-soybean systems to diversified crop rotations reduces reliance on pesticides and fertilizers, cutting contamination at the source rather than trying to filter it out downstream.
• Cover Crop Implementation: Planting cover crops during off-seasons captures excess nitrogen in the soil, preventing it from leaching into groundwater and surface water supplies.
• Organic and Perennial Systems: Shifting to organic management and perennial crop systems has consistently shown substantial reductions in both nitrate and pesticide pollution while improving soil health and farm resilience.
• Policy and Investment Reform: Safeguarding drinking water requires policy reforms and investments that enable farmers to adopt proven practices that protect both community health and long-term sustainability, rather than relying on voluntary programs.

Research from the Rodale Institute demonstrates that these in-field, system-level solutions have consistently shown substantial reductions in nitrate and pesticide pollution while improving soil health and farm resilience. The transition is not just environmentally necessary; it is economically justified. Despite their widespread use, research has shown that neonicotinoids have little economic benefit to farmers, yet they continue to contaminate water supplies and harm human health.

The path forward requires moving beyond treating contaminated water after the fact. As agricultural pollution continues to degrade water quality, particularly in the Midwest, the scientific evidence points to a single conclusion: protecting drinking water means transforming agricultural practices from the ground up, not just installing better filters at the treatment plant.